1. Field of the Invention
The present invention relates to an electric connecting structure and a method for fabricating the same and, more particularly, to an electric connecting structure comprising preferred oriented Cu6Sn5 grains and a method for fabricating the same.
2. Description of Related Art
Copper (Cu) is generally used in metal connecting devices (for examples, metal interconnects, under bump metallizations (UBMs), Cu pillar, or through silicon via (TSV) because of its high electrical conductivity and thermal transferring ability.
For instance, when Cu is applied in the UBM of a packaging structure, UBM is frequently electrically connected to other electronic elements through soldering. The process for connecting UBM to other electronic elements requires high-temperature reflow process, and intermetallic compounds (IMCs) may be generated in the reaction between copper and solder.
As shown in FIG. 1, the conventional flip-chip solder joint structure comprises two chips 11, 12, wherein each chip 11, 12 respectively has electrical pads 13, 14 made of Cu, and the electrical pads 13, 14 electrically connect to each other through a solder 17. After a reflow process, Cu atoms contained in the electrical pads 13, 14 may diffuse into the solder 17 and react with tin (Sn) atoms contained in the solder 17, so that partial solder 17 is transformed into IMC layers 171, 172. More specifically, the IMC layers 171, 172 are respectively formed between the solder 17 and the electrical pads 13, 14. In this case, the formed IMC layers 171, 172 may cause the reliability of the flip-chip solder joint structure reduced.
Currently, in order to improve the property of the solder joints, one means is to reduce the thickness of the IMC layer. For example, a barrier layer is disposed between the electrical pad and the solder to prevent the growth of the IMC layer, as shown in U.S. Pat. No. 6,867,503 B2. However, the barrier layer causes the manufacturing cost of the electronic device increased, and the reliability thereof may be reduced.
Therefore, it is desirable to provide a novel electric connecting structure, in order to improve the property of solder joints and reduce the manufacturing cost thereof,